JP2021169248A - Vehicular steering system - Google Patents

Abstract

To supply a highly practical left and right independently turnable steering system.SOLUTION: In a vehicular steering system including a pair of wheel turning apparatuses that mutually independently turn left and right wheels, and a controller that controls the pair of wheel turning apparatuses, the controller is designed so that a turn quantity ratio R that is a ratio of a turn quantity ψO of the left wheels to a turn quantity ψI of the right wheels is varied depending on a vehicle speed v and a change rate ΔR of the turn quantity ratio is limited based on an extent of a change in the vehicle speed (ΔRLIM).SELECTED DRAWING: Figure 5

Description

The present invention relates to a steering system mounted on a vehicle and steering the left and right wheels independently.

In a steering system capable of independently steering the left and right wheels (hereinafter, may be referred to as "left and right independent steering type steering system"), for example, as described in the following patent document, the traveling speed of the vehicle (hereinafter, may be referred to as "left and right independent steering type steering system"). Hereinafter, there is a technique for changing the ratio of the steering amount of the left and right wheels (hereinafter, sometimes referred to as the "steering amount ratio") according to the "vehicle speed"). More specifically, according to the parallel geometry in which the steering amounts of the left and right wheels are equal when the vehicle speed is high, the steering amount of the turning outer wheels is smaller than the steering amount of the turning inner wheels when the vehicle speed is low. According to the geometry, the left and right wheels are steered to ensure a good balance between turning stability and small turning performance.

JP-A-2019-171908

When changing the steering amount ratio of the left and right wheels according to the vehicle speed, when the vehicle is accelerating or decelerating, and when the degree of acceleration or deceleration is large, the steering amount ratio changes significantly. It is also expected that the driver will feel uncomfortable due to changes in behavior. Therefore, it is possible to improve the practicality of the left-right independent steering type steering system by making improvements. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a highly practical vehicle steering system.

In order to solve the above problems, the vehicle steering system of the present invention is used.
A vehicle steering system including a pair of wheel steering devices that steer the left and right wheels independently of each other and a controller that controls the pair of wheel steering devices.
The controller
The steering amount ratio, which is the ratio of the steering amount of the left and right wheels, is changed based on the vehicle speed, and the change speed of the steering amount ratio is limited based on the degree of change in the vehicle speed. It is characterized by.

According to the vehicle steering system of the present invention (hereinafter, may be simply referred to as "steering system"), the change speed of the steering amount ratio is limited based on the degree of change in vehicle speed, so that the behavior changes. It is suppressed that the driver feels uncomfortable due to the above. As a result, the steering system of the present invention becomes a highly practical steering system.

Aspects of the invention

The "steering amount" of a wheel can be considered as an angle change from a position when traveling straight, that is, a steering angle. In that sense, the "steering amount ratio" of the left and right wheels can be considered as the steering angle ratio, and a large steering amount ratio means that the difference between the steering amounts of the left and right wheels is large. A small amount ratio can be defined as a small difference in the amount of steering between the left and right wheels. According to the definition, "change of steering amount ratio based on vehicle speed" can be set so that, for example, the steering amount ratio becomes larger as the vehicle speed is higher. Specifically, the steering amount ratio can be a ratio according to the Ackermann ratio, which will be described in detail later. Furthermore, the steering amount ratio can be set so that the steering amount of the left and right wheels that are the turning outer wheels is smaller than the steering amount of the left and right wheels that are the turning inner wheels. can.

As a specific embodiment, in the steering system of the present invention, for example, the steering amount of one of the left and right wheels is determined based on the steering request, and the steering amount of the other of the left and right wheels is determined to the left and right. It may be configured to be determined based on the steering amount of one of the wheels and the steering amount ratio set based on the vehicle speed. Then, when such a configuration is adopted, the change in the steering amount of the other of the left and right wheels with respect to the steering amount of the one of the left and right wheels is limited based on the degree of change in the vehicle speed. The change speed of the steering amount ratio may be limited.

The "degree of change in vehicle speed" can be considered as a change in vehicle speed per unit time, that is, a change speed in vehicle speed. As a parameter that indicates the degree of change in vehicle speed, for example, the acceleration in the front-rear direction occurring in the vehicle (a positive value when accelerating, a deceleration when decelerating, and a negative value). That is, the front-rear acceleration of the vehicle and the controlling driving force applied to the vehicle (a concept including the driving force when accelerating and the braking force when decelerating) can be considered. The speed of changing the steering amount ratio in the present invention may be limited based on those parameters.

In view of the above-mentioned effect of suppressing the discomfort given to the driver, it is desirable that the limit of the change speed of the steering amount ratio is larger when the degree of change in vehicle speed is high than when it is low. Further, for example, when the degree of change in vehicle speed exceeds the set first degree, the steering amount ratio is fixed, and then when the degree of change becomes lower than the first degree and becomes the second degree or less. It may be allowed to change the steering amount ratio below the setting change speed.

It is a schematic diagram which shows the whole structure of the vehicle which mounted the steering system for a vehicle of 1st Example. It is a perspective view which shows the wheel arrangement module which incorporated the wheel steering apparatus which constitutes the vehicle steering system of 1st Embodiment. It is a graph explaining the steering amount ratio of the left and right wheels. It is a graph for demonstrating the limitation about the change speed of the steering amount ratio of the left and right wheels in the vehicle steering system of 1st Embodiment. It is a graph which shows the change of the steering amount of a wheel with respect to the change of the vehicle speed in the steering system for a vehicle of 1st Example. It is a flowchart of the steering control control program executed in the vehicle steering system of 1st Embodiment. It is a flowchart of the wheel steering program executed in the vehicle steering system of 1st Embodiment. It is a flowchart of the steering angle ratio determination subroutine executed in the steering integrated control program executed in the steering system for a vehicle of 1st Embodiment. It is a graph which shows the change of the steering amount of a wheel with respect to the change of the vehicle speed in the steering system for a vehicle of 2nd Example. It is a flowchart of the steering angle ratio determination subroutine executed in the steering integrated control program executed in the steering system for vehicles of 2nd Example.

Hereinafter, as a mode for carrying out the present invention, a vehicle steering system according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition to the following examples, the present invention will be carried out in various forms with various modifications and improvements based on the knowledge of those skilled in the art, including the forms described in the section of [Aspects of the Invention]. be able to.

[A] Overall configuration of a vehicle equipped with a vehicle steering system The steering system of the first embodiment has left and right front wheels 10FL and 10FR and left and right rear wheels 10RL and 10RR as schematically shown in FIG. It is installed in the vehicle. The left and right front wheels 10FL and 10FR are the driving wheels and the steering wheels. When it is not necessary to distinguish the left and right front wheels 10FL and 10FR, they are collectively referred to as the front wheel 10F, and when it is not necessary to distinguish the left and right rear wheels 10RL and 10RR, they are collectively referred to as the rear wheel 10R. However, when it is not necessary to distinguish between the front wheels 10F and the rear wheels 10R, they may be simply collectively referred to as the wheels 10.

This steering system is a so-called steer-by-wire type steering system, and is operated with a pair of wheel steering devices 12 provided for each of the two front wheels 10F in order to steer the two front wheels 10F independently of each other. An operating device 14 for accepting a person's operation and a pair of steering electronic control units (hereinafter, may be abbreviated as "steering ECU") 16 for controlling each pair of wheel steering devices 12. , And an operation electronic control unit (hereinafter, may be abbreviated as "operation ECU") 18 for controlling the operation device 14 and controlling the steering ECU 16. The configuration and control of the steering system will be described in detail later, but it can be considered that the controller of the steering system is configured by the two steering ECUs 16 and the operation ECU 18.

Further, the vehicle is equipped with a vehicle drive system including a pair of wheel drive units 20 provided on each of the two front wheels 10F and rotationally driving each of them by an electric motor. The vehicle drive system includes an accelerator pedal 22 as an accelerator operating member operated by the driver, an accelerator operating amount sensor 24 for detecting the operating amount of the accelerator pedal 22, and an accelerator detected by the accelerator operating amount sensor 24. It includes a vehicle drive electronic control unit (hereinafter, may be abbreviated as "drive ECU") 26 that controls the operation of a pair of wheel drive units 20 based on the amount of operation. Since the vehicle drive system has a general configuration and general control is performed, the description of the configuration and control of the vehicle drive system will be omitted.

Further, the vehicle is provided with a hydraulic braking system. The brake system has a hydraulic fluid consisting of a brake pedal 30 as a brake operating member operated by the driver, a master cylinder 32 connected to the brake pedal 30, a pump, and the like, and pressurizes the hydraulic fluid. A supply device 34, four brake devices 36 provided on each of the four wheels for braking by the pressure of the hydraulic fluid from the hydraulic fluid supply device 34, and a brake electron that controls the operation of the hydraulic fluid supply device 34. It includes a control unit (hereinafter, may be referred to as a "brake ECU") 38. The brake system is a so-called brake-by-wire system, and the brake ECU 38 has a hydraulic fluid supply device 34 to each wheel 10 based on the brake operation amount which is the operation amount of the brake pedal 30 detected by the brake operation amount sensor 40. By controlling the pressure of the hydraulic fluid supplied to the brake device 36 of the above, the braking force applied to the vehicle is controlled. Since the brake system has a general configuration and general control is performed, the description of the configuration and control of the brake system will be omitted.

The vehicle is provided with a CAN (car area network or controllable area network) 44, and two steering ECUs 16, an operation ECU 18, a drive ECU 26, and a brake ECU 38 are connected to the CAN 44. The ECUs 16, 18, 26, and 38 execute the control to be performed by each of the ECUs 16, 18, 26, and 38 while communicating with each other via the CAN 44. By the way, each of the ECUs 16, 18, 26, 38 drives a computer having a CPU, ROM, RAM, etc., and components (for example, an electric motor, a valve, a pump, etc.) based on the instructions of the computer. It is configured to include the driver (drive circuit) of. The vehicle is provided with a front-rear acceleration sensor 46 for detecting the front-rear acceleration, which is the acceleration in the front-rear direction occurring in the vehicle, and the wheel rotation speed of each of the rear wheels 10R ( A wheel speed sensor 48 for detecting _{v W (} which may be referred to as “wheel speed” hereafter) is provided. The front-rear acceleration sensor 46 and the wheel speed sensor 48 are also connected to the CAN 44.

[B] Hardware Configuration of Vehicle Steering System Each of the pair of wheel steering devices 12 of the vehicle steering system of this embodiment is incorporated in the wheel arrangement module 50. The wheel arrangement module 50 also incorporates one of the pair of wheel drive units 20 of the vehicle drive system described above and one of the four brake devices 36 of the brake system. The wheel arrangement module (hereinafter, may be simply abbreviated as “module”) 50 is a module for arranging the wheel 10b on which the tire 10a is mounted on the vehicle body, as shown in FIG. The wheel 10b itself can be considered as a wheel, but in the present embodiment, the wheel 10b on which the tire 10a is mounted is referred to as a wheel 10.

Explaining the wheel steering device 12 of this steering system while explaining the configuration of the module 50, the above-mentioned wheel drive unit 20 arranged in the module 50 has a housing 20a and a drive built in the housing 20a. It has an electric motor as a source, a speed reducer that reduces the rotation of the electric motor (both not shown), and an axle hub (hidden and invisible in the figure) to which the wheel 10b is attached. The wheel drive unit 20 is arranged inside the rim of the wheel 10b, and is a so-called in-wheel motor unit. Since the wheel drive unit 20 has a well-known structure, the description of the structure will be omitted.

The module 50 includes a MacPherson type suspension device (also referred to as a "MacPherson strut type"). In this suspension device, the housing 20a of the wheel drive unit 20 functions as a carrier for holding the wheels rotatably, and further, the housing 20a functions as a steering knuckle in the wheel steering device 12, and vertical movement with respect to the vehicle body is allowed. Will be done. Therefore, the suspension device includes a lower arm 52 which is a suspension arm, a housing 20a of the wheel drive unit 20, a shock absorber 54, and a suspension spring 56.

Since the suspension device itself has a general structure, the lower arm 52 has a so-called L-arm shape, and the base end portion is divided into two parts in the front-rear direction of the vehicle. At its base end, it is rotatably supported by a side member (not shown) of the vehicle body via the first bush 58 and the second bush 60 so as to be rotatable around the arm rotation axis LL. The housing 20a of the wheel drive unit 20 is provided at a lower portion thereof via a first joint, an arm connecting ball joint 62 (hereinafter, may be referred to as “first joint 62”), at the tip of the lower arm 52. It is rotatably connected.

The lower end of the shock absorber 54 is fixedly supported by the housing 20a of the wheel drive unit 20, and the upper end is supported by the upper portion of the tire housing of the vehicle body via the upper support 64. The upper end of the suspension spring 56 is also supported by the upper portion of the tire housing of the vehicle body via the upper support 64, and the lower end of the suspension spring 56 is supported by the lower support 54a provided in a flange shape on the shock absorber 54. ing. That is, the suspension spring 56 and the shock absorber 54 are arranged in parallel with each other between the lower arm 52 and the vehicle body.

As described above, the module 50 has a brake device 36, and the brake device 36 straddles the disc rotor 66, which is attached to the axle hub together with the wheel 10b and rotates with the wheel 10, and the disc rotor 66. This is a disc brake device including a brake caliper 68 held in the housing 20a of the wheel drive unit 20. Although detailed description is omitted, the brake caliper 68 has a brake pad as a friction member and a hydraulic cylinder, and the brake device 36 is a hydraulic fluid supplied from the hydraulic fluid supply device 34 to the hydraulic cylinder. By pressing the brake pad against the disc rotor 66 depending on the pressure of the wheel 10, a braking force for stopping the rotation of the wheel 10 is generated.

The wheel steering device 12 is a single-wheel independent steering device for steering only one of a pair of left and right wheels 10 independently of the other, and is generally used as a steering knuckle as described above. The housing 20a of the functioning wheel drive unit 20 (hereinafter, may be referred to as "steering knuckle 20a" when treated as a component of the wheel steering device 12) and the lower arm at a position close to the base end portion of the lower arm 52. It is configured to include a steering actuator 70 arranged in 52 and a tie rod 72 connecting the steering actuator 70 and the steering knuckle 20a.

The steering actuator 70 is rotated by the rotation of the steering motor 70a, which is an electric motor as a drive source, the reduction gear 70b that reduces the rotation of the steering motor 70a, and the steering motor 70a via the reduction gear 70b. It is configured to include an actuator arm 70c that functions as a pitman arm. The base end portion of the tie rod 72 is connected to the actuator arm 70c via a ball joint 74 for connecting the base end portion of the rod, which is a second joint (hereinafter, may be referred to as “second joint 74”), and the tie rod 72 The tip portion is connected to the knuckle arm 20b of the steering knuckle 20a via a rod tip portion ball joint 76 (hereinafter, may be referred to as “third joint 76”) which is a third joint.

In the wheel steering device 12, the line connecting the center of the upper support 64 and the center of the first joint 62 is the kingpin axis KP. By operating the steering motor 70a, the actuator arm 70c of the steering actuator 70 rotates around the actuator axis AL, as shown by the thick arrow in the figure. The rotation is transmitted by the tie rod 72, and the steering knuckle 20a is rotated around the kingpin axis KP. That is, as shown by the thick arrow in the figure, the wheel 10 is steered. Due to such a structure, the wheel steering device 12 includes an actuator arm 70c, a tie rod 72, a knuckle arm 20b, and the like, and a motion conversion mechanism 78 that converts the rotational motion of the steering motor 70a into the steering motion of the wheels 10. It is equipped with.

In the wheel steering device 12, a steering actuator 70 is arranged on the lower arm 52. Therefore, the work of assembling the module 50 to the vehicle body can be easily performed. Simply put, the suspension device, brake device, and wheel steering device are mounted on the vehicle simply by attaching the base end of the lower arm 52 to the side member of the vehicle body and attaching the upper support 64 to the upper part of the tire housing of the vehicle body. You can do it. That is, the module 50 is considered to be a module having excellent mountability on a vehicle.

The operating device 14 has a general structure in a steer-by-wire type steering system. Briefly, as shown in FIG. 1, the steering wheel 80 as a steering operating member operated by the driver. A steering sensor 82 for detecting the steering operation angle, which is the rotation angle of the steering wheel 80, as an operation amount from the straight-ahead position of the steering operation member, and a reaction force applying device for applying an operation reaction force to the steering wheel 80. It is configured to include 84 and. The reaction force applying device 84 includes a reaction force motor 84a, which is an electric motor as a force source, and a speed reducer 84b for transmitting the force of the reaction force motor 84a to the steering wheel 80.

[C] Control of vehicle steering system
i) Basic control In this steering system, the operating ECU 18 determines the target steering angle ψ _L ^* of the left front wheel 10FL and the target steering angle ψ _R ^* of the right front wheel as the target of the steering amount of each front wheel 10F. Based on these target steering angles ψ _L ^* and ψ _R ^* , a pair of steering ECUs 16 control the wheel steering device 12 corresponding to each of them to control the left front wheel 10FL and the right front wheel 10FR, respectively. Steer so that the steering angles ψ _L and ψ _R are the target steering angles ψ _L ^* and ψ _R ^* .

More specifically, the operation ECU 18 has a target vehicle body slip angle β _S ^* _{which is a vehicle body slip angle β S} to be realized in the vehicle body based on the steering request, that is, the steering operation angle δ acquired by the steering sensor 82. To determine. By the way, when the vehicle is automatically driven, information about the _{target vehicle body slip angle β S} ^* is sent from the automatic driving system (not shown) as a steering request via CAN44. Based on the target vehicle body slip angle β _S ^* , the operating ECU 18 may refer to which of the left and right front wheels 10FL and 10FR is the turning outer wheel (the wheel far from the turning center, hereinafter referred to as “turning outer ring 10FO”. (Yes), and it is determined which is the turning inner ring (the wheel on the side closer to the turning center, hereinafter may be referred to as "turning inner ring 10FI").

The operation ECU 18 determines the target steering angles ψ _L ^* and ψ _R ^* , which are _{the targets of the steering angles ψ L} and ψ _R of the left and right front wheels 10FL and 10FR, respectively. _{To change the ratio R of the steering angles ψ L} and ψ R (hereinafter, sometimes referred to as the “steering angle ratio”) R as the ratio of the steering amount of the wheels (steering amount ratio) according to the vehicle speed v. In addition, the operation ECU 18 determines the target steering angles ψ _L ^* and ψ _R ^* based on the steering angle ratio R set in advance based on the vehicle speed v.

Here, the steering angle ratio R will be described in detail with reference to FIG. If the steering angle of the turning outer ring 10FO is defined as ψ _O and the steering angle of the turning inner ring 10FI _{is defined as ψ I} , the steering angle ratio R is, for example,
R = ψ _O / ψ _I
Can be defined as.

FIG. 3A schematically shows a steering state according to a so-called parallel geometry. In this steering state, roughly speaking, the steering angle ψ _O of the turning outer ring 10FO and the turning of the turning inner ring 10FI are shown. The steering angle ψ _I is equal to each other, and the steering angle ratio R is “1”. Orientation of the inner turning wheel 10FI is the perpendicular to the line connecting the center C _I of the ground plane of the turning center TC and the turning inner wheel 10FI, the orientation of the turning outer 10FO the ground plane of the turning outer 10FO swirling around TC It is not perpendicular to the line connecting the center _{CO of.} In this steering system, for convenience, the steering angle ψ _I of the turning inner ring 10FI and the vehicle body slip angle β _S are treated to be equal to each other.

On the other hand, FIG. 3B schematically shows a steering state according to the so-called Ackermann geometry, and roughly speaking, the direction of the turning inner ring 10FI is the contact patch of the turning center TC and the turning inner ring 10FI. become perpendicular to the line connecting the center C _I of and the orientation of the turning outer 10FO has a perpendicular to the line connecting the center C _O of the ground plane of the turning center TC and the turning outer wheel 10FO. Therefore, the turning angle ψ _{O of the turning outer ring 10FO is smaller than the turning angle ψ I} of the turning inner ring 10FI, and the turning angle ratio R is the Ackermann turning which is a specific value in this turning state. The rudder angle ratio is _RA .

The Ackermann ratio A can be considered as 0% in the steering state according to the parallel geometry and 100% in the steering state according to the Ackermann geometry. Incidentally, the relationship between the Ackermann ratio A and the steering angle ratio R can be expressed by the following equation.
A = (1-R) / (1- _RA ) x 100%

When the Ackermann ratio A is high, slippage of the tire 10a during turning of the vehicle can be suppressed, wear of the tire 10a, and squeal noise (cue) generated by the tire 10a can be suppressed. On the other hand, when the Ackermann rate A is low, the turning performance of the vehicle is improved. Simply put, the running of the vehicle will be snappy (sporty). In view of these, in the present steering system, the operation ECU 18 changes the steering angle ratio R in order to change the Ackermann ratio A according to the vehicle speed v.

FIG. 3C is a graph showing the relationship between the vehicle speed v and the steering angle ratio R, and as shown in this graph, the operation ECU 18 sets the steering angle ratio R as the vehicle speed v increases. Larger, conversely, the lower the vehicle speed v, the smaller the steering angle ratio R. More specifically, when the vehicle speed v is _{equal to or less than the lower limit vehicle speed v L} (for example, 20 km / h), the steering angle ratio R is set to the Ackermann steering angle ratio _RA , and the vehicle speed v is the upper limit vehicle speed v _U (for example). , 100 km / h) or more, set to 1, respectively, _{and when it is between the lower limit vehicle speed v L} and the upper limit vehicle speed v _U , the Ackermann steering angle ratio R increases as the vehicle speed v increases. Set so that it approaches 1 from _A.

Based on the target vehicle body slip angle β _S ^* described above, the operation ECU 18 sets the target inner wheel steering angle ψ _I ^{* , which is the target steering angle ψ *} of the turning inner ring 10FI, according to the following equation.
ψ _I ^* = β _S ^*
Based on the target inner wheel steering angle ψ _I ^* and the vehicle speed v, the steering angle ratio R is specified with reference to the map data as shown in FIG. 3 (c), and then a steering angle ratio R specified that, based on the target inner steering angle [psi _I ^* turning inner 10FI, the target outer steering angle [psi _O ^* is the target steered angle [psi _O ^* turning outer 10FO , According to the following formula
ψ _O ^* ＝ ψ _I ^* × R
decide. _{Incidentally, the operation ECU 18 determines the vehicle speed v for each wheel speed v W} of the front wheels 10F depending on the rotation speed of the drive motor of the wheel drive unit 20, and each wheel of the rear wheels 10R depending on the detection of the wheel speed sensor 48. Identify based on speed v _W.

When the left front wheel 10FL is the turning outer ring 10FO, the operation ECU 18 sets the left wheel target turning angle ψ _L ^{* , which is the target turning angle ψ *} of the left front wheel 10FL, to ψ _O ^* and the target turning of the right front wheel 10FR. The right wheel target turning angle ψ _R ^* , which is the steering angle ψ ^* _{, is determined as ψ I} ^* , and when the right front wheel 10FR is the turning outer ring 10FO, the left wheel target turning angle ψ _L ^* is set to ψ. Determine the right wheel target steering angle ψ _R ^* for _I ^* _{and ψ O} ^* , respectively. The operation ECU 18 transmits information about the determined target steering angles ψ _L ^* and ψ _R ^* to each of the two steering ECUs 16 corresponding to the left and right front wheels 10F via the CAN 44.

Each steering ECU 16 controls the wheel steering device 12 corresponding to itself so that the steering angle ψ of the front wheels 10F corresponding to itself becomes the transmitted target steering angle ψ ^* . More specifically, since the wheel steering device 12 does not have a steering angle sensor for directly detecting the steering angle ψ of the wheels 10, in this steering system, the steering angle ψ of the wheels 10 Utilizing the fact that there is a specific relationship between and the rotation angle of the steering motor 70a (hereinafter, may be referred to as “motor rotation angle”) θ, the steering ECU 16 uses the motor rotation angle of the steering motor 70a. The steering force generated by the steering actuator 70 is controlled based on θ. Since the steering force generated by the steering actuator 70 is equivalent to the steering torque Tq, which is the torque generated by the steering motor 70a, specifically, the steering ECU 16 should generate the steering motor 70a. ^{The target steering torque Tq *} , which is the steering torque Tq, is determined based on the motor rotation angle θ of the steering motor 70a. Incidentally, the motor rotation angle θ can be considered as the displacement angle of the motor shaft from the state when the vehicle goes straight, and is accumulated over 360 °.

Specifically, the determination of the target steering torque Tq ^* will be specifically described. For each wheel 10, the steering ECU 16 has a target motor rotation angle θ, which is a target of the motor rotation angle θ, based on the ^{target steering angle ψ *. *} Determine. The steering motor 70a is a brushless DC motor, and has a motor rotation angle sensor (for example, a Hall IC, a resolver, etc.) for phase switching in supplying current to itself. Based on the detection of the motor rotation angle sensor, the steering ECU 16 grasps the actual motor rotation angle θ, which is the current motor rotation angle θ with reference to the reference motor rotation angle. The steering ECU 16 obtains the motor rotation angle deviation Δθ, which is the deviation of the actual motor rotation angle θ with respect to the target motor rotation angle θ ^{*, and based on this motor rotation angle deviation Δθ (= θ *} −θ), according to the following equation. The target steering torque Tq ^* is determined.
Tq ^* = _GP · Δθ + G _D · (dΔθ / dt) + G _I · ∫Δθdt
The above equation is an equation according to the feedback control law based on the motor rotation angle deviation Δθ, and the first term, the second term, and the third term are the proportional term, the differential term, the integral term, _GP , respectively. G _D and G _I are proportional gain, differential gain, and integral gain, respectively.

The steering torque Tq and the supply current I to the steering motor 70a have a specific relationship. In other words, since the steering torque Tq depends on the force exerted by the steering motor 70a, the steering torque Tq and the supply current I are generally in a proportional relationship. According to this, the steering ECU 16 determines ^{the target supply current I *} , which is the target of the supply current I to the steering motor 70a, based on ^{the determined target steering torque Tq *,} and sets the target supply current I ^* . , Supply to the steering motor 70a.

ii) Restriction on change of steering angle ratio and change of steering angle According to the above-mentioned basic control, in short, the steering angle ratio R of the left and right front wheels 10F is changed according to the vehicle speed v. NS. For example, during braking and acceleration, the vehicle speed v may change significantly, and when the vehicle speed v changes at a high speed, the change speed of the steering angle ratio R also increases, and the steering angle ψ _{O of the turning outer ring 10FO also increases.} Will change relatively quickly. This change in the steering angle ψ _O becomes an unintended change in the lateral force acting on the vehicle, which leads to disturbance of the behavior of the vehicle and giving the driver a sense of discomfort. Therefore, in this steering system, a limit is set for changing the steering angle ratio R.

More specifically, if the speed at which the steering angle ratio R is changed is defined as the steering angle ratio changing speed ΔR, in this steering system, the operating ECU 18 has the steering angle ratio changing speed ΔR as the change speed limit value ΔR _LIM. The steering angle ratio R is determined so as not to exceed the above, and the target steering angle of the turning outer ring 10FO is determined based on the steering angle ratio R thus determined.

Specifically, as will be described later, the operation ECU 18 executes the steering control control program at a constant time pitch, and determines the steering angle ratio R for each execution of the program. As described above, the operation ECU 18 _{determines the steering angle ratio R based on the target inner wheel steering angle ψ I} ^* and the vehicle speed v with reference to the above map data. The steering angle ratio R is determined. Is the standard steering angle ratio _RS , which is a temporary steering angle ratio. Operation ECU18 is a steering angle ratio R that is finally determined by the last execution of the program, identified as the previous steering angle ratio R _PRE, standard turning angle ratio for the previous steering angle ratio R _PRE R _{The difference in S} is specified as the amount of change in the steering angle ratio R per the execution time pitch of the program, that is, the steering angle ratio changing speed ΔR. When the absolute value of the steering angle ratio change speed ΔR _{exceeds the change speed limit value ΔR LIM} , the operation ECU 18 imposes a limit on the change of the steering angle ratio R. More specifically, the steering angle ratio change speed ΔR is suppressed within the _{change speed limit value ΔR LIM.}

In this steering system, the operating ECU 18 refers to the map data as shown in the graph of FIG. 4 based on the front-rear acceleration Gx detected by the front-rear acceleration sensor 46 arranged in the vehicle for _{the change speed limit value ΔR LIM.} To decide. When the front-rear acceleration Gx is a positive value, it indicates that the vehicle is accelerating, and when it is a negative value, it indicates that the vehicle is decelerating. As can be seen from the graph, the change speed limit value ΔR _LIM is set smaller as the absolute value of the front-rear acceleration Gx increases in both acceleration and deceleration. That is, the more sudden acceleration and deceleration, the greater the restriction on the change of the steering angle ratio R.

Specifically, when the absolute value of the steering angle ratio changing speed ΔR _{is equal to or less than the changing speed limit value ΔR LIM} , the operating ECU 18 maintains the steering angle ratio changing speed ΔR. On the other hand, when the absolute value of the steering angle ratio change speed ΔR _{exceeds the change speed limit value ΔR LIM} , the steering angle ratio change speed ΔR is _{replaced with the change speed limit value ΔR LIM} during acceleration, and during deceleration. Then, the steering angle ratio change speed ΔR is replaced with the inverted _{value of the change speed limit value ΔR LIM.} The operation ECU 18 adds the steering angle ratio change speed ΔR thus maintained or replaced to the above-mentioned front rotation steering angle ratio R _PRE to obtain the steering angle ratio R in the execution of the program this time. decide.

_{The change in the steering angle ψ O} of the turning outer ring 10FO with respect to the change in the vehicle speed v when the vehicle _{body slip angle β S} is constant under the limitation of the steering angle ratio change speed ΔR as described above is a graph shown in FIG. become that way. When the vehicle speed v _{higher than the upper limit vehicle speed v U} is decelerated by a relatively large deceleration Gx, that is, a relatively large braking force is applied and the first speed v _{1 is reached through the upper limit vehicle speed v U} , that is, Between time t ₁ and time t ₂ , the absolute value of the steering angle ratio change speed ΔR is relatively large, as shown by the broken line, and the change gradient _{of the steering angle ψ O of the turning outer ring 10FO, as shown by the broken line.} Is relatively large. On the other hand, when the above limitation is applied, the absolute value of the steering angle ratio change speed ΔR is relatively small, and _{the change in the steering angle ψ O} of the turning outer ring 10FO, that is, the change in the steering angle ratio R is relatively small. Become gradual. After that, _{when the vehicle reaches a stop after passing the lower limit speed v L} at a relatively small deceleration Gx from _{time t 2} , if there is no limit, the absolute value of the steering angle ratio change speed ΔR is as shown by the broken line. relatively small, the turning angle [psi _O ie steering angle ratio R of the turning outer wheel 10FO until vehicle speed v reaches the lower limit vehicle speed v _L, i.e., until time t _3, changes relatively slowly. Even if there is a limit, the absolute value of the steering angle ratio change speed ΔR is relatively small, and the steering angle ψ _O of the turning outer ring 10FO, that is, the steering angle ratio R is compared until _{time t 4} which is later than _{t 3.} It changes slowly.

Similarly, when the vehicle is _{accelerated from a vehicle speed v lower than the lower limit vehicle speed v L with a} relatively large acceleration Gx, that is, when a relatively large driving force is applied and the vehicle reaches the second speed v _{2 through the lower limit vehicle speed v L.} That is, _{between time t 5} and time t ₆ , the absolute value of the steering angle ratio change speed ΔR is relatively large as shown by the broken line, and the steering angle ψ _O of the turning outer ring 10FO is as shown by the broken line. The change gradient is relatively large. On the other hand, when the above limitation is applied, the absolute value of the steering angle ratio change speed ΔR is relatively small, and _{the change in the steering angle ψ O} of the turning outer ring 10FO, that is, the change in the steering angle ratio R is relatively gradual. Become. After that, _{when the vehicle speed v rises through the upper limit speed v U} at a relatively small acceleration Gx from _{time t 6} , if there is no limit, the absolute value of the steering angle ratio change speed ΔR is compared as shown by the broken line. _{The steering angle ψ O,} that is, the steering angle ratio R of the turning outer ring 10FO is relatively small, and changes relatively slowly _{until the vehicle speed v reaches the upper limit vehicle speed v U} , that is, until the time t _7. Even if there is a limit, the absolute value of the steering angle ratio change speed ΔR is relatively small, and the steering angle ψ _O of the turning outer ring 10FO changes relatively slowly until time t ₈ later than time t _7. ..

As described above, by limiting the steering angle ratio change speed ΔR based on the front-rear acceleration Gx, even if the vehicle speed v changes significantly during deceleration or the vehicle speed v changes significantly during acceleration, the vehicle turns. The steering angle ratio R changes gently. Therefore, it is possible to effectively suppress the disturbance of the behavior of the vehicle and the feeling of strangeness to the driver.

iii) Control flow In the control of the steering system described above, the computer of the operation ECU 18 performs the steering control control program shown in the flowchart in FIG. 6, and the computer of each steering ECU 16 shows the wheel steering shown in the flowchart in FIG. Each program is executed repeatedly at a short time pitch (for example, several msec to several tens of msec). The control flow of the steering system will be briefly described below by explaining the processes according to the flowcharts of those programs.

In the process according to the steering control control program, first, in step 1 (hereinafter, abbreviated as "S1". The same applies to other steps), it is determined whether or not automatic operation is in progress. If the vehicle is not in automatic driving, the steering operation angle δ is acquired by the detection of the steering sensor 82 in S2, and the target vehicle body slip angle β _S ^* is determined based on the steering operation angle δ in S3. During automatic driving, in S4, the target vehicle body slip angle β _S ^* is acquired based on the information from the automatic driving system.

Subsequently, in S5, which of the left and right front wheels 10FL and 10FR is the turning outer ring 10FO and which is the turning inner ring 10FI based on the target vehicle body slip angle β _S ^{*, specifically, the code thereof.} It is determined. Then, in S6, the target vehicle body slip angle β _S ^* is determined to be the target inner wheel steering angle ψ _I ^*.

In the next S7, a steering angle ratio determining process for determining the steering angle ratio R is performed. This steering angle ratio determination process is performed by executing the steering angle ratio determination subroutine shown in the flowchart in FIG. In the process according to this subroutine, first, in S21, the current vehicle speed v is specified based on _{the wheel speed v W of each wheel 10.} In the following S22, based on the vehicle speed v and the determined target inner wheel steering angle ψ _I ^* _{, the above-mentioned standard steering angle ratio RS} is obtained with reference to the map data as shown in FIG. 3C. _{Determined, and in S23, the front rotation steering angle ratio R PRE,} which is the steering angle ratio R finally determined in the previous execution of the program, is specified. Then, in S24, by subtracting the front rotation steering angle ratio R _{PRE from the determined standard steering angle ratio RS} , the amount of change in the steering angle ratio R per the execution time pitch of the program, that is, the steering angle. The ratio change rate ΔR is determined.

_{In the following S25, the change speed limit value ΔR LIM} was determined with reference to the map data as shown in FIG. 4 based on the longitudinal acceleration Gx acquired by the detection of the longitudinal acceleration sensor 46, and was determined in S26. It is determined whether or not the absolute value of the steering angle ratio change speed ΔR is _{larger than the change speed limit value ΔR LIM.} When the absolute value of the steering angle ratio change speed ΔR is _{larger than the change speed limit value ΔR LIM} , the sign of the front-rear acceleration Gx is determined in S27. That is, it is determined whether or not the value of the front-rear acceleration Gx indicates that acceleration is in progress. When accelerating (including the case where the vehicle speed v is maintained), in S28, the steering angle ratio change speed ΔR is limited to the change speed limit value ΔR _LIM , and when deceleration is in progress. , S29, the steering angle ratio change speed ΔR is limited to the one in which the sign of _{the change speed limit value ΔR LIM is inverted.} When it is determined in S26 that the absolute value of the steering angle ratio changing speed ΔR is equal to _{or less than the changing speed limit value ΔR LIM} , the steering angle ratio changing speed ΔR is maintained at the value determined in S24.

Based on the steering angle ratio change speed ΔR determined as described above, in S30, the _{steering angle ratio changing speed ΔR is added to the front rotation steering angle ratio R PRE} , so that the rotation in the execution of the program this time is performed. The steering angle ratio R is determined, and in S31, the steering angle ratio R is set as the front rotation steering angle ratio R _PRE in the next execution of the program.

After the processing according to the subroutine is completed, the target outer wheel steering angle ψ _O ^* is determined in S8 based on the steering angle ratio R determined as described above by the processing. In the next S9, it is determined whether or not the left front wheel 10FL is a turning outer ring, and when the left front wheel 10FL is a turning outer ring, in S10, the left wheel target turning angle ψ _L ^* is the target outer wheel turning angle ψ. _{If O} ^* and the right wheel target steering angle ψ _R ^* are the target inner _{wheel steering angle ψ I} ^* and the left front wheel 10FL is not the turning outer wheel, the left wheel target steering angle ψ _L ^* is the target in S11. The inner wheel steering angle ψ _I ^* and the right wheel target steering angle ψ _R ^* are defined as the target outer wheel steering angle ψ _O ^* . Then, in S12, the information about the left wheel target steering angle ψ _L ^* and the right wheel target steering angle ψ _R ^* determined in this way is transmitted to the steering ECU 16 corresponding to the left front wheel 10FL and the right front wheel 10FR, respectively. Will be sent.

In the process according to the wheel steering program executed by each steering ECU 16 ^{, information about the target steering angle ψ *} of the corresponding front wheel 10F is received from the operation ECU 18 in S41, and the target steering angle ψ in S42. ^{Based on *} , the target motor rotation angle θ ^{* of} the steering motor 70a is determined. In the following S43, the actual motor rotation angle θ, which is the actual rotation angle of the steering motor 70a, is acquired, and in S44, the motor rotation angle deviation Δθ, which is the deviation of the actual motor rotation angle θ with respect to the ^{target motor rotation angle θ *, is determined.} Will be done. ^{In the next S45, the target steering torque Tq *} is determined according to the above equation based on the motor rotation angle deviation Δθ, and in S46, it should be supplied to the steering motor 70a based on the ^{target steering torque Tq *. The target supply current I *,} which is the current, is determined. Then, in S47, a current is supplied to the steering motor 70a based on the ^{target supply current I *.}

The vehicle steering system of the second embodiment is the same as the vehicle steering system of the first embodiment in the hardware configuration, and the control regarding the steering of the front wheels 10F is limited only to the limitation of changing the steering angle ratio R. It is different. In view of this, the description of the steering system of the second embodiment will be given only with respect to the restriction on the change of the steering angle ratio R.

In the steering system of the first embodiment, the operating ECU 18 _{determines the change speed limit value ΔR LIM} based on the detected front-rear acceleration Gx, and suppresses the steering angle ratio change speed ΔR _{within the change speed limit value ΔR LIM.} Therefore, the change of the steering angle ratio R was restricted. On the other hand, in the steering system of the second embodiment, the operation ECU 18 operates the brake operation amount ε _B and the accelerator pedal 22 which are the operation amounts of the brake pedal 30 based on the brake operation and the accelerator operation. based on the accelerator operation amount epsilon _a is the amount, the braking force applied to the vehicle F _B and the driving force F _D (hereinafter sometimes collectively referred to as "longitudinal force F") to estimate its longitudinal force Based on F, it is added to the change of the steering angle ratio R.

Specifically, in the operating ECU 18, when the estimated braking force F _B exceeds the first set braking force F _B1 set to a relatively large value, and when the estimated driving force F _D becomes a relatively large value. When the set first set driving force F _D1 is exceeded (hereinafter, it may be collectively referred to as "when the controlling driving force F exceeds the first set driving force F _{1"), the vehicle speed v} It is determined that the degree of change exceeds the first degree, and the value of the steering angle ratio R is fixed. Next, when the estimated braking force F _B becomes equal to or less than the second set braking force F _B2 set to a value smaller than the first set braking force F _B1 , and the estimated driving force F _D is the first set drive. _{When the second set driving force F D2} or less is set to a value smaller than the force F _D1 (hereinafter, collectively referred to as "when the control driving force F becomes the second set control driving force F _{2 or less".} (In some cases), it is determined that the degree of change in vehicle speed v is less than the second degree, which is set lower than the first degree, and the fixed change speed limit value ΔR _LIM (strictly--) as the setting change speed. It is permissible to change the steering angle ratio R below (ΔR _LIM). That is, the steering angle ratio R is relatively gently brought closer _{to the standard steering angle ratio RS.} Incidentally, the change speed limit value ΔR _LIM may be set to a different value when the vehicle is accelerating and when the vehicle is decelerating.

Under the above-mentioned restrictions on the change of the steering angle ratio R, the change of _{the steering angle ψ O} of the turning outer ring 10FO with respect to the change of the vehicle speed v when the vehicle _{body slip angle β S} is constant is shown in the graph shown in FIG. Will be. When the vehicle is decelerated by a relatively large braking operation from a vehicle speed v higher than the upper limit vehicle speed v _U , that is, a relatively large braking force is applied to the vehicle and the speed v _{1 is reached through the upper limit vehicle speed v U} , that is, If there is no above limitation between time t ₁ and time t ₂ , the absolute value of the steering angle ratio change speed ΔR is relatively large, that is, the steering angle ψ _{O of the turning outer ring 10FO, as shown by the broken line.} The change gradient of is relatively large. In contrast, when there is the limit, because the braking force F _B which is applied is greater than the first set braking force F _B1, steering angle ratio R, i.e., the steering angle [psi _O turning outer 10FO is It does not change. From time t _2, the loosening of the brake operation, in a state in which the braking force F _B and smaller than the second set braking force F _B2 to impart, when the vehicle through the lower velocity v _L reaches the vehicle is stopped, if there is no restriction, As shown by the broken line, the absolute value of the steering angle ratio change speed ΔR is relatively small, and the steering angle ψ _O of the turning outer ring 10FO, that is, the steering angle ratio R, is such that the vehicle speed v reaches the lower limit vehicle speed v _L. , until the time t _3, to change relatively slowly. Even when there is a limit, the steering angle ratio change speed ΔR is _{relatively low as the change speed limit value −ΔR LIM, and the steering angle ψ O} of the turning outer ring 10FO, that is, the steering angle ratio R is later than _{t 3.} up to t _4, to change relatively slowly.

Similarly, when the vehicle is accelerated by a relatively large accelerator operation from a vehicle speed v lower than the lower _{limit vehicle speed v L} , that is, a relatively large driving force is applied and the speed v ₂ is reached _{via the lower limit vehicle speed v L.} That is, _{between time t 5} and time t ₆ , if there is no above limitation, as shown by the broken line, the steering angle ratio change speed ΔR is relatively high, and the change gradient of _{the steering angle ψ O of the turning outer ring 10FO is.} Relatively large. In contrast, when there is the restriction, since the driving force F _D being applied is greater than the first set drive force F _D1, the steering angle ratio R, i.e., the steering angle [psi _O turning outer 10FO is It does not change. After that, from time t ₆ , there is no limit when the vehicle speed v rises through the upper limit speed v _U in a state where the accelerator operation is loosened and the applied driving force F _D is smaller than the second set driving force F _{D 2.} In this case, as shown by the broken line, the absolute value of the steering angle ratio change speed ΔR is relatively small, and the steering angle ψ _O of the turning outer ring 10FO, that is, the steering angle ratio R is such that the vehicle speed v reaches the upper limit vehicle speed v _U. , in other words, until the time t _7, to change relatively slowly. Even when there is a limit, the steering angle ratio change speed ΔR is _{relatively low as ΔR LIM, and the steering angle ψ O} of the turning outer ring 10FO, that is, the steering angle ratio R is until _{time t 8} which is later than _{time t 7.} It changes relatively slowly.

As described above, by limiting the steering angle ratio change speed ΔR based on the estimated control driving force F, even if the vehicle speed v changes significantly during deceleration, the vehicle speed v changes significantly during acceleration. However, the steering angle ratio R changes slowly. Therefore, also in the steering system of the present embodiment, it is possible to effectively suppress the disturbance of the behavior of the vehicle and the feeling of strangeness to the driver.

Also in the steering system of the second embodiment, the operation ECU 18 repeatedly executes the steering control control program shown in the flowchart in FIG. 6, and the program is the steering angle ratio determination process of S7, that is, the steering angle ratio. Only the decision flowchart is different from the steering control control program executed in the steering system of the first embodiment. The steering angle ratio determination subroutine executed in the steering system of the second embodiment shows a flowchart in FIG. 10, and in the following description, only the flow of processing according to the flowchart will be briefly described.

In the process according to the steering angle ratio determination subroutine executed in the steering system of the second embodiment, first, in S51, the current vehicle speed v is specified based on _{the wheel speed v W of each wheel 10.} In the following S52, based on the vehicle speed v and the determined target inner wheel steering angle ψ _I ^* _{, the above-mentioned standard steering angle ratio RS} is obtained with reference to the map data as shown in FIG. 3 (c). _{Determined, and in S53, the front rotation steering angle ratio R PRE,} which is the steering angle ratio R finally determined in the previous execution of the program, is specified. Then, in S54, by subtracting the front rotation steering angle ratio R _{PRE from the determined standard steering angle ratio RS} , the amount of change in the steering angle ratio R per the execution time pitch of the program, that is, the steering angle. The ratio change rate ΔR is determined.

_{In the following S55, the braking force F B} or the braking force applied to the vehicle is applied based on _{the brake operation amount ε B} detected by the brake operation amount sensor 40 _{or the accelerator operation amount ε A} detected by the accelerator operation amount sensor 24. driving force F _D is, i.e., the estimated longitudinal force F is, in S56, the value of the large longitudinal force flag FL is whether "1" is determined. Large longitudinal force flag FL, the initial value is "0", when the steering angle ratio relatively large braking force F _B or relatively large driving force F _D is being applied to the vehicle R is fixed In other words, it is a flag whose value is set to "1" when the change of the steering angle ratio R is prohibited.

When the large control driving force flag FL is not "1", it is determined in S57 whether or not the _{control driving force F is larger than the first set control driving force F 1.} When the control driving force F is _{larger than the first set control driving force F 1} , the large control driving force flag FL is set to "1" in S58, and the value of the steering angle ratio change speed ΔR is set to "1" in S59. It is set to 0 ". That is, the change of the steering angle ratio R is prohibited, in other words, the steering angle ratio R is fixed to the current value.

If it is determined in S56 that the large control driving force flag FL is already set to "1", S57 and S58 are skipped, and in S59, the value of the steering angle ratio change speed ΔR is "0". Is maintained at. When it is determined in S57 that the control driving force F is _{not larger than the first set control driving force F 1} , the value of the steering angle ratio change speed ΔR determined in S54 is maintained.

In the following S60, it is determined whether or not the control driving force F is equal to or less than the second control driving force F ₂ set to be smaller than the first set control driving force F _1. When the control driving force F is _{equal to or less than the second control driving force F 2} , the large control driving force flag FL is reset to "0" in S61. Then, in the next S62, it is determined whether or not the absolute value of the steering angle ratio change speed ΔR is _{larger than the change speed limit value ΔR LIM.} When the absolute value of the steering angle ratio change speed ΔR is _{larger than the change speed limit value ΔR LIM} , in S63, it is determined whether the vehicle is braking or driving (accelerating) based on the control driving force F. When driving, the steering angle ratio change speed ΔR is limited to the change speed limit value ΔR _LIM in S64, and when braking, the steering angle ratio change speed ΔR is set in S65. The change speed limit value ΔR _LIM is limited to the inverted sign. When the absolute value of the steering angle ratio change speed ΔR is equal to or less than the change speed limit value ΔR _{LIM, the steering angle ratio change speed ΔR is not restricted.} When it is determined in S60 that the control driving force F _{is not equal to or less than the second control driving force F 2} , and the value of the large control driving force flag FL is "1", the value of the steering angle ratio change speed ΔR is ". It is maintained at 0 ”. On the other hand, when the value of the large control driving force flag FL is “0”, the value of the steering angle ratio change speed ΔR determined in S54 is maintained.

Then, in S66, the steering angle ratio change speed ΔR determined as described above _{is added to the front} rotation steering angle ratio R PRE to determine the steering angle ratio R, which is determined in S67. The steering angle ratio R is defined as the front rotation steering angle ratio R _PRE in the next execution of the program.

10: Wheels 12: Wheel steering device 14: Operation device 16: Steering electronic control unit (steering ECU) [Controller] 18: Operation electronic control unit (operation ECU) [Controller] 20: Wheel drive unit 36: Brake device 46: Front-rear acceleration sensor 50: Wheel arrangement module 52: Lower arm 70: Steering actuator 70a: Steering motor 72: Tie rod 78: Motion conversion mechanism 80: Steering wheel [Steering operating member] 82: Steering sensor ψ: Wheel rolling Steering angle [steering amount] ψ _O : turning outer wheel steering angle ψ _I : turning inner wheel steering angle R: steering angle ratio [steering amount ratio] ΔR: steering angle ratio change speed ΔR _LIM : change speed limit Value v: Vehicle running speed (vehicle speed) v _L : Lower limit vehicle speed v _U : Upper limit vehicle speed Gx: Front-rear acceleration F: Control driving force F ₁ : First set control drive force F ₂ : Second set control drive force

Claims (9)

A vehicle steering system including a pair of wheel steering devices that steer the left and right wheels independently of each other and a controller that controls the pair of wheel steering devices.
The controller
A vehicle configured to change the steering amount ratio, which is the ratio of the steering amounts of the left and right wheels, based on the vehicle speed, and to limit the changing speed of the steering amount ratio based on the degree of change in the vehicle speed. For steering system. The controller
The steering amount of one of the left and right wheels is determined based on the steering request, and the steering amount of the other of the left and right wheels is determined based on the determined steering amount of one of the left and right wheels and the vehicle speed. It is configured to be determined based on the set steering amount ratio, and is also configured.
The change speed of the steering amount ratio is limited by limiting the change in the steering amount of the other of the left and right wheels with respect to the steering amount of the one of the left and right wheels based on the degree of change in the vehicle speed. The vehicle steering system according to claim 1, which is configured as described above. The vehicle steering system according to claim 1 or 2, wherein the controller limits the change speed of the steering amount ratio based on the front-rear acceleration of the vehicle that indicates the degree of change in vehicle speed. .. The vehicle according to claim 1 or 2, wherein the controller is configured to limit the change speed of the steering amount ratio based on a control driving force on the vehicle that indicates the degree of change in vehicle speed. Steering system. The vehicle according to any one of claims 1 to 4, wherein the controller makes the limit of the change speed of the steering amount ratio larger when the degree of change in vehicle speed is high than when it is low. Steering system for. The controller
When the degree of change in vehicle speed exceeds the set first degree, the steering amount ratio is fixed, and then when the degree of change becomes lower than the first degree and becomes the second degree or less, the setting change speed is set. The vehicle steering system according to any one of claims 1 to 4, which is configured to allow the following changes in the steering amount ratio. The vehicle steering system according to any one of claims 1 to 6, wherein the steering amount ratio is set larger as the vehicle speed is higher. The vehicle steering system according to any one of claims 1 to 7, wherein the steering amount ratio is a ratio according to the Ackermann ratio. Claim 1 in which the steering amount ratio is set so that the steering amount of the left and right wheels that are the turning outer wheels is smaller than the steering amount of the left and right wheels that are the turning inner wheels. The vehicle steering system according to any one of claims 8.

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